What Are the Common Post-Processing Steps Required for Ti-6Al-4V LENS 3D Printed Parts?

Stress Relief and Thermal Treatment

LENS-printed Ti-6Al-4V components require immediate stress relief annealing at 650-750°C in a vacuum or inert atmosphere to prevent distortion and cracking caused by significant residual stresses from the directed energy deposition process. This is typically followed by Hot Isostatic Pressing (HIP) at 900-930°C with 100-150 MPa pressure to eliminate internal porosity, lack-of-fusion defects, and achieve near-full density (>99.5%). A subsequent solution treatment and aging cycle optimizes the microstructure—transforming the martensitic α' phase formed during rapid solidification into a balanced α+β structure with improved mechanical properties and stability.

Support Structure Removal and Surface Preparation

The removal of support structures and surface preparation are critical initial steps. Supports are typically removed using wire EDM or precision cutting tools to avoid damaging the base material. The as-printed LENS surface, characterized by partially melted powder particles and surface roughness (Ra 15-30μm), requires abrasive blasting with aluminum oxide or glass beads to clean and uniform the surface. For components requiring superior surface finish, vibratory finishing or flow polishing may be employed to reduce surface roughness to Ra 2-4μm, particularly important for medical implants or aerodynamic surfaces.

Precision Machining and Geometric Correction

Precision CNC machining is essential to achieve final dimensional tolerances and critical surface specifications. Typical stock allowances of 1-3mm are removed from all functional surfaces to eliminate the heat-affected surface layer and achieve the required geometric accuracy. Multi-axis CNC systems perform contour following operations, while specialized techniques like deep hole drilling create precise internal features. Due to titanium's poor thermal conductivity and tendency to work-harden, machining employs optimized parameters, specialized tooling, and high-pressure coolant systems to maintain surface integrity.

Surface Enhancement and Performance Optimization

Additional surface treatments enhance specific performance characteristics. Shot peening introduces compressive surface stresses that improve fatigue strength by 50-100% and resistance to stress corrosion cracking. For medical implants or fluid system components, electropolishing creates a smooth, biocompatible surface while simultaneously passivating the titanium to enhance corrosion resistance. For aerospace components subjected to fretting wear, specialized coatings or surface hardening treatments may be applied to critical contact areas.

Quality Validation and Certification

Comprehensive quality assurance validates that post-processed LENS components meet all specifications. This includes dimensional verification using CMM scanning, mechanical testing to confirm tensile strength (typically 900-1100 MPa) and elongation (10-15%), and microstructural examination to ensure proper α+β phase distribution. Non-destructive testing methods—including ultrasonic inspection for internal defects and fluorescent penetrant inspection for surface flaws—ensure component integrity. For critical applications in aerospace and medical sectors, additional certification including chemical analysis and traceability documentation completes the quality assurance process.